The present invention relates to a lubricating composition such as a lubricant, a lubricating grease, and a rust preventive oil for use in a torque limiter, and a ball-and-roller bearing. More particularly, the present invention relates to a lubricating composition used for machine parts of a business machine including a synthetic resin molded product as peripheral parts; the lubricating composition preventing chemical attacks to the synthetic resin molded product.
A torque limiter is one of the machine parts of business machine, and is used in a paper feed mechanism, and a tension mechanism including a ribbon and a sheet. For example, torque is produced by utilizing tightening and binding force in a radial direction to an inner ring of a spring, and by pressing and sliding a friction board with the spring in a thrust direction. In either case, friction force is used to produce torque.
To prevent wear, abnormal exothermicity, abnormal sound of seizing and the like between the inner ring of the torque limiter and the spring or the friction board, and between the friction boards, a lubricating oil or grease is used.
Generally, the inner ring of the torque limiter is made of sintered metal material, which is immersed in the lubricant or the grease.
A typical lubricant or lubricating grease for the torque limiter often comprises a mineral oil, alkylnaphthalene, or an ester as a base oil, and various additives such as an anti-wear agent depending on applications. The torque limiter is required to have and maintain an oil film on its parts for a long period of time. Performance of the bearing depends on how a metal contact is suppressed, and a friction coefficient is stabilized. In particular, the torque limiter used in the paper feed mechanism of a copy machine or a printer, or the tension mechanism of the ribbon and the sheet requires the lubricant that keeps variance of the torque extremely low, and does not produce a metal contact sound.
The peripheral parts of the torque limiter are made of a non-crystalline resin having good moldability such as polycarbonate and an ABS resin. Such resin may be subjected to chemical attacks by a contact with an oil or its vapor resulting from a leak of the lubricant used in the torque limiter. The chemical attack is a phenomenon that microstreaks propagate on a surface of the resin to cause hair cracks, crazing, cracks, and surface roughness, resulting in breakage of the resin board.
Commercially available lubricants may have the following problems: the oil film is broken at early stage to cause an abnormal sound, or even if the abnormal sound is not produced, torque is reduced because a friction reducing effect is too high. At the paper feed of the copy machine or the printer, the torque limiter is used as a paper moving mechanism utilizing torque attributed to the torque limiter. Problematic reduction in torque and production of the abnormal sound are caused by wear of a friction surface for a prolonged use, and shear of the lubricant. When the business machine is frequently used, viscosity of the lubricant is reduced by exothermic, thereby lowering its performance. If the lubricant used in the torque limiter is leaked or vaporized to outside of the torque limiter for any reasons, the peripheral parts, especially non-crystalline material such as polycarbonate and the ABS resin, may be subjected to chemical attacks. Therefore, it is urged to provide a lubricant having excellent chemical attack resistance. The existing lubricants using naphthene based mineral oil having an aromatic ring in the molecule, alkylnaphthalene, or alkyldiphenylether as a base oil have high ability to produce the oil film, and satisfy torque performances required for the torque limiter. Such lubricant comprising the aromatic ring or a polar group in the molecule as the base oil can attack the non-crystalline resin material. There is no lubricant satisfying both the lubricating performance (torque performance) and chemical attack resistance required for the torque limiter.
At a fixing portion of a copy machine or a printer utilizing an electrophotographic apparatus, a ball-and-roller bearing is widely used to support rotatably the fixing roller. At the fixing portion, a toner charged and attached to a paper is pressed at about 250xc2x0 C. at the maximum to be fixed to the paper. Thus, the ball-and-roller bearing supporting the roller at the fixing portion is often used at high temperature. In particular, a heat roll has a heater inside of a hollow axis, and is heated inside. Correspondingly, the bearing may also be used at a temperature of exceeding 200xc2x0 C. The ball-and-roller bearing for supporting the heat roll may be used via an adiabatic sleeve made of a resin in order to decrease the temperature of the bearing. Nevertheless, a temperature of an end face of the bearing may reach about 200xc2x0 C. by an effect of radiant heat.
One example of the conventional lubricating composition for use in the ball-and-roller bearing used at the high temperature is grease for prelubricating. The grease is typically fluorinated grease for prelubricating because it is less deteriorated at a high temperature, and provides prolonged life.
In recent years, as the demand for the electrophotographic apparatus increases, reduction in costs becomes a problem to be solved urgently. However, the aforementioned fluorinated grease is too expensive to reduce the costs of the ball-and-roller bearing used in the fixing roller of the electrophotographic apparatus.
In order to reduce the costs of the electrophotographic apparatus, there have been widely used parts made of non-crystalline resin, i.e., polycarbonate resin having both of moldability and heat resistance. Such resin is easily suffering from so-called chemical attacks by fats and oils used in the grease for prelubricating.
As an alternative of the fluorinated grease, there is used an urea grease comprising a high viscosity ester oil as the base oil. The urea grease is also used at high temperature, and is more inexpensive than the fluorinated grease. However, the urea grease easily induces chemical attacks to the polycarbonate resin. For the purpose of reduction in costs, a high viscosity ester oil is added to the fluorinated grease, undesirably resulting in a lowered dropping point.
Examples of rust preventive oil for the torque limiter and the ball-and-roller bearing include NP-0, NP-3, and NP-6 rust preventive oils in accordance with JIS K2246 (rust preventive oil).
The rust preventive oil generally includes light mineral oils. If the bearing is used while the rust preventive oil remains on a surface of the bearing, the peripheral resin molded parts are easily subjected to chemical attacks.
An object of the present invention is to provide a lubricating composition capable of preventing chemical attacks to machine parts of a business machine including a synthetic resin molded product. Examples of the machine parts of the business machine include a torque limiter, a ball-and-roller bearing and the like. Examples of the lubricating composition include a lubricant, a lubricating grease, a rust preventive oil and the like.
According to one aspect of the present invention, a lubricating composition having chemical attack resistance for a synthetic resin molded product comprises a base oil, and a compounding agent, wherein the base oil is at least one synthetic saturated hydrocarbon oil selected from the group consisting of a poly-xcex1-olefin, and an ethylene-xcex1-olefin copolymer.
According to other aspect of the present invention, a lubricating composition comprises at least two lubricating greases selected from the group consisting of three types of lubricating greases each having a different base oil; the first lubricating grease comprising as the base oil at least one synthetic saturated hydrocarbon oil selected from the group consisting of a poly-xcex1-olefin, and an ethylene-xcex1-olefin copolymer, and at least one thickener selected from the group consisting of an urea compound, silica powder, and bentonite powder; the second lubricating grease comprising a perfluoro polyether oil as the base oil, and fluororesin powder as a thickener; and the third lubricating grease comprising an alkyldiphenylether oil as the base oil, and at least one thickener selected from the group consisting of an urea compound, silica powder, and bentonite powder.
According to still other aspect of the present invention, a rust preventive oil which works as a lubricating composition comprises a base oil, a rust preventive agent, and an antioxidant, wherein the base oil is at least one synthetic saturated hydrocarbon oil selected from the group consisting of a poly-xcex1-olefin, and an ethylene-xcex1-olefin copolymer, wherein the rust preventive agent is at least one metal salt selected from the group consisting of a metal salt of sulfonic acid, and a metal salt of a monocarboxylic acid, and wherein the antioxidant is a phenol based antioxidant.
Conventional rust preventive oils include as a base oil a low boiling point solvent such as kerosene and mineral spirits, a low viscosity lubricant, and a mineral oil such as wax. Conventional lubricating greases include as a base oil mineral oils, alkylnaphthalene, ester and the like. A factor of a chemical attack to the polycarbonate resin has been investigated. It has been discovered that not mineral oils including a single component, but mineral oils including multiple components, especially low boiling point components, easily induce chemical attacks. The present invention is made based on such discovery. The base oil is at least one synthetic saturated hydrocarbon oil selected from the group consisting of a poly-xcex1-olefin, and an ethylene-xcex1-olefin copolymer, whereby no chemical attacks to the synthetic resin molded product is induced.